A small stream that flows along a cave passage that was enlarged to its current size by an earlier, larger stream. Commonly underfit streams are found flowing under vadose conditions along the floors of drained phreatic tubes, long abandoned by the phreatic flow that enlarged them. Underfit streams may also occur if the major flow in a vadose streamway is captured to lower levels by the opening of a new shaft. The main flow no longer uses the downstream passages, leaving any tributaries to amalgamate as an underfit stream [9].